1. Field of the Invention
The present invention relates to a reversible thermosensitive recording medium and a reversible thermosensitive recording member having the reversible thermosensitive recording medium.
2. Description of the Related Art
Conventionally, the following thermosensitive recording medium has been widely known: the thermosentitive recording medium that uses a color reaction between an electron-donating color-forming compound (also referred to as “color former or leuco dye,” hereinafter) and an electron-accepting compound (also referred to as “developer,” hereinafter). As OA has advanced, the thermosensitive recording medium has become widely used as output paper of facsimile, word processors, and scientific measurement machines, and more recently as magnetic thermosensitive cards such as prepaid cards and point cards. As for such a thermosensitive recording medium in practical use, in terms of environmental concerns, an overhaul of how to recycle and reduce the amount used and other issues is urgently sought. However, because the coloring thereof is irreversible, it is not possible to delete a once-recorded image and repeatedly use. Moreover, among a few things that can be done is to add new information to a portion where no image is recorded; a recordable portion is limited in size. The fact is that the amount of information to be recorded is reduced, and that a new card is created after a recording area runs out. Against the backdrop of garbage and deforestation problems of recent years, it is hoped to develop a reversible thermosensitive recording medium that can be rewritten any number of times.
The problem with such a reversible thermosensitive recording medium is that, when an under layer is provided between a support and a reversible thermosensitive recording layer, a crack is more likely to occur. In view of this, there has been proposed a reversible thermosensitive recording medium having a protective layer (overcoat layer) made of highly flexible ultraviolet curing resin and having a tan δ peak temperature of 155° C. or lower (or a temperature at which dynamic relaxation occurs) (see Japanese Patent Application Laid-Open (JP-A) No. 11-334220). However, since the heat resistance is low, the durability decreases. Another problem is that residues adhere to a heat source such as a thermal head.
The applicant of the present application has previously proposed a reversible thermosensitive recording medium that includes a support, a thermosensitive recording layer on the support, and a protective layer on the thermosensitive recording layer, wherein the thermosensitive recording layer contains an electron-donating color-forming compound and an electron-accepting compound, the tone of color changes depending on temperatures in a reversible manner, and the protective layer contains a polymer of compositions including two types of acrylate compound, which are selected from among acrylate compounds having a pentaerythritol group and acrylate compounds having a dipentaerythritol group (see JP-A No. 2007-331382).
However, even the above proposal does not have performance sufficient enough in terms of all the following properties: durability, crack resistance, and resistance to formation of residue on the head (head-residue resistance). It is currently hoped to make further improvements and development.